1. Field of the Invention
The present invention relates to an apparatus for controlling an automotive vehicle, more specifically, an engine, an automatic transmission and other devices of the vehicle. More particularly, the present invention is concerned with means for preventing an interference between running stability control means and controls of various devices in power transmitting system of the vehicle.
2. Discussion of the Prior Art
An automotive vehicle may fall in an unstable running condition with the lateral road gripping capacity of a wheel tire being exceeded during turning of the vehicle on a road surface having a relatively low friction coefficient, or at a relatively high speed, or to clear an obstacle, for example. The unstable running condition may be an oversteering or understeering tendency of the vehicle. The oversteering tendency is caused when the road gripping force of the rear wheels is considerably smaller than that of the front wheels, resulting in an excessively larger turning angle of the vehicle than the steering angle, and leading to a spinning tendency of the vehicle. On the other hand, the understeering tendency is caused when the road gripping force of the front wheels is considerably smaller than that of the rear wheels, resulting a considerably smaller turning angle of the vehicle than the steering angle.
To cope with such running instability of the vehicle, there has been proposed a turning stability control apparatus for stabilizing the vehicle turning behavior, for instance, a vehicle stability control system (VSC system) as disclosed in JP-A-4-266538. Such a turning stability control apparatus is activated when the vehicle turning condition is unstable, namely, when an oversteering or understeering tendency of the vehicle is detected. Described in detail, the apparatus is adapted to reduce the engine output and at the same time apply a braking force to the front or rear wheels, for producing a moment to reduce the oversteering or understeering tendency of the vehicle, thereby to stabilize the turning behavior attitude of the vehicle.
In the automotive vehicle equipped with such a turning stability control apparatus, there are encountered various sorts of drawbacks due to interferences or inadequate coordination between an operation of the turning stability control apparatus, and control operations of various devices of the power transmitting system, such as: a fluid-operated power transmitting device (e.g., torque converter) incorporating a direct-coupling clutch (e.g., lock-up clutch); an automatic transmission; and a differential limiting clutch.
For instance, the following drawbacks are conventionally encountered:
(1) Where the turning stability control apparatus is adapted to control a throttle valve of the engine or a braking device for improving the turning stability of the vehicle, and a controller for the power transmitting system is adapted to effect a learning control of the system, an operation of the turning stability control apparatus may cause the learning control to be effected erroneously, and the erroneous learning control of the power transmitting system leads to an unstable operation of the system, which may cause a shock to be generated in the power transmission path.
(2) Where the turning stability control apparatus is adapted to control the engine output torque thereby to control the vehicle drive force, the vehicle drive force cannot be controlled with sufficiently high accuracy by the engine output control by the turning stability control device, when the automatic transmission is in the process of a shifting action, or when the control mode of the lock-up clutch is changed, since an inertia torque is generated during the shifting action of the automatic transmission, and the torque ratio of the torque converter varies due to a change in the control mode of the lock-up clutch.
(3) Where a controller for the automatic transmission is adapted to inhibit a shifting action of the automatic transmission (hold it in the same operating position) during turning of the vehicle or during running of the vehicle on an uphill or downhill road, while the turning stability control apparatus is adapted to reduce the throttle valve opening or shift up the automatic transmission as well as reduce the throttle valve opening, the operation of the turning stability control apparatus may interfere with the operation of the automatic transmission controller, that is, the turning stability control apparatus may command the automatic transmission to be shifted up while the automatic transmission controller commands the automatic transmission to be held in the same operating position.
(4) Where the turning stability control apparatus is operated, upon generation of the excessive understeering tendency, to reduce the throttle valve opening to reduce the engine output and at the same time apply a brake to the front wheel on the outer side of the vehicle turning path, the power transmitting system may suffer from a shock due to a change in the engine speed caused by the reduction of the throttle valve opening and the brake application to the front wheel.
(5) Where the turning stability control apparatus is adapted to hold the automatic transmission in a predetermined operating position or shift up the automatic transmission and change the throttle valve opening by an amount corresponding to an expected amount of reduction of the vehicle drive force caused by the holding or shift-up action of the automatic transmission, the vehicle drive force may become inadequate to improve the vehicle turning stability in the event where the automatic transmission cannot be shifted to the predetermined position or cannot be shifted up, for some reason or other.
(6) Where the turning stability control apparatus is adapted to hold the automatic transmission in the predetermined position and inhibit a shifting action thereof, the automatic transmission may be shifted down or up immediately after the inhibition of the shifting action is cancelled. In this case, the shift-down action of the automatic transmission may cause a shifting shock under some running condition of the vehicle, or the shift-up action may cause a decrease in the vehicle drive force unexpectedly to the vehicle operator under some vehicle running condition.